This invention relates to methods and apparatus for fusing electric conductors together, and more particularly to such methods and apparatus when employed in making dynamo-electric machines such as electric motors and generators.
Fusing (also sometimes referred to as hot staking) is a well known process used in the manufacture of dynamo-electric machines for such purposes as mechanically and electrically connecting the leads of armature coils to tangs on or slots in the commutator of the armature. Fusing may similarly be used for mechanically and electrically connecting stator coil leads to terminations on the stator. The typical fusing process involves the application of force and heat to at least one of two (or more) electrical conductors to be connected. The heat removes insulation (e.g., wire insulation) from the conductors. The heat also helps to soften the conductors so that they can be more easily deformed into close and intimate contact with one another. Force is used (as the foregoing suggests) to deform the conductors into intimate contact with one another.
A fusing operation is typically carried out by placing a fusing electrode and a ground electrode in contact with at least one of the conductors to be connected. Heat is generated by passing an electrical current through the series circuit including the fusing electrode, the workpiece, and the ground electrode. The fusing electrode is forced against the workpiece to produce the workpiece deformation required as part of the fusing operation.
While it is important to ensure that there is enough heat and force to remove all insulation and produce a tight mechanical and electrical connection, it is also important to avoid any significant melting of the conductors during the fusing operation. It may also be important to avoid overheating dynamo-electric machine structures adjacent to the fusing site. For example, commutator bars being fused to coil leads may be embedded in a mass of resin which it is important not to overheat.
In recent years increasing attention has been given to the fusing step or steps involved in the manufacture of dynamo-electric machines. This has been due to several factors such as the desire to improve the quality of fused connections, the desire to increase production rates, and the need to avoid overheating of the more heat-sensitive resin materials now being used in place of asbestos materials to support the commutator bars in armatures. Reducing fusing cycle time tends to increase production rates and may help avoid overheating of adjacent structures, but it may also make it more difficult to maintain or improve the quality of the resulting connections. At the very least, shorter fusing cycle time requires more careful control of the parameters of the fusing cycle in order to ensure that the desired mechanically tight connections of low electrical resistance with no residual insulation remaining in the connection are produced.
In view of the foregoing, it is an object of this invention to facilitate the provision of shorter, more efficient fusing cycles.
It is another object of this invention to provide improved controls for fusing operations so that the quality of the resulting connections can be improved and/or so that the time required to perform a fusing cycle can be reduced.